Pleated filter cartridges with annular pleated filter elements, sometimes referred to as corrugated filters, are used in various liquid filtration applications involving the removal of particulates from liquid streams, such as aqueous liquid streams. Such pleated filter cartridges are removably mountable in liquid-handling apparatus, and are removed and replaced as necessary to maintain desired filtering capabilities.
The variety of liquid filtration applications in industry is great, involving a wide variety of liquid streams, many of which are aqueous liquid streams with a great variety of chemical and particulate constituents in them. Pleated filter cartridges of various diameters, lengths and constructions are used in different applications involving many different liquid streams (aqueous-based and otherwise) and many different kinds of liquid-handling devices.
Pleated filter cartridges typically include an inner rigid perforate tube-like core around which an annular pleated filter element is disposed. The ends of the annular pleated filter element are in sealing engagement with a pair of endcaps, at least one of which has a central aperture in flow communication with the inside of the tube-like core. When mounted in liquid-handling apparatus, the outer circumference of the pleated filter cartridge is typically in contact with the liquid to be filtered. The liquid is filtered as it flows through the annular pleated filter element and into the perforate core. The filtered liquid exits the core through one of the endcaps.
The prior art includes information on a great variety of pleated filter cartridges made using a variety of configurations and a variety of different filter materials and filter material combinations. Among the filter materials are certain non-woven materials, woven materials, fiberglass materials, expanded (or foamed) materials, and various paper-like materials. Sheets of various non-woven materials, primarily polypropylene, nylon and various polyesters, are frequently used as pleated filter materials. Thicknesses of non-woven sheets for pleated annular filter elements usually range from about 0.28 mm to about 0.48 mm, but pleated non-woven filter materials as thin as about 0.17 mm have been used. In some cases, one or more open mesh or net layers are used in pleated structures for spacing, support or flow-facilitating purposes.
Despite the great amount of development activity which has occurred in the field of pleated annular filter cartridges, there are a number of significant continuing problems, needs and shortcomings in the field.
There is a continuing need for pleated annular filter cartridges with a pleated structure having an increased surface area for a given circumferential dimension of the pleated element—or, stated differently, increased filter surface area for a filter of given diameter. In this connection, many pleated filter elements of the prior art have multiple filtering layers, sometimes including different layers for “pre-filtering” and filtering purposes. A common practice is to include in the pleated element a number of layers of the same or differing pore sizes pleated together, usually with coarser layers on the upstream side (i.e., typically the outer side) and the finer layers on the downstream side, so that the coarser layers remove the larger particulates first and the finer layers remove the smallest particulates last. In some cases, the plural layers must be spaced slightly from one another to provide room for accumulation of particulates. These factors limit the pleat density (i.e., the number of pleats for a given circumferential dimension), and thus tend to limit the area of the pleated structure accessible to liquid flow.
Another shortcoming of certain annular pleated filter cartridges of the prior art is the requirement of frequent replacement—i.e., replacement at intervals shorter than may be desired. There is a continuing, well-understood need for improved pleated annular filter elements and cartridges with extended useful lives.
The problem of short life spans of pleated annular filter cartridges, i.e., the need for frequent replacement, in some cases is due in part to limitations in the ability to periodically remove accumulated particulates, such as by backwashing or other filter cleaning operations. There is a continuing need for pleated annular filter cartridges which readily release accumulated particulates, and thereby allow extended usefulness. In certain cases, the filtering materials degrade too quickly in the liquid stream and become unable to function effectively. There is a continuing need for pleated annular filter cartridges which can stand up to liquid streams in filtration without degrading for extended periods of effective filtering, including under intense conditions.
Another on-going need is for pleated filter cartridges able to withstand certain liquid streams—i.e., cartridges which are compatible with such liquid streams. For example, in some cases certain non-woven materials (e.g., polypropylene) widely used in pleated filter cartridges are susceptible to degradation caused by gamma radiation in certain liquid streams. There is a need for improved annular pleated filter elements which are resistant to such degradation in certain liquid streams.
Another concern with certain commercially-available pleated filter cartridges is that they are quite expensive, a concern which is exacerbated by the above-noted need for frequent replacement. There is a need for highly-effective, long-lasting pleated filter cartridges which are relatively inexpensive.
Other pertinent background information which is useful in understanding this invention is included in the detailed descriptions section of this document.